Transcript Pion yield studies for proton drive beams of 2-8 GeV kinetic energy for stopped muon and low-energy muon decay experiments Sergei Striganov Fermilab Workshop on Applications.

Pion yield studies for proton drive beams
of 2-8 GeV kinetic energy for stopped
muon and low-energy muon decay
experiments
Sergei Striganov
Fermilab
Workshop on Applications of High Intensity
Proton Accelerators
Fermilab
October 19-21, 2009
Task
 Long targets with small radius
made from heavy material are
usually used for low energy
pion/muon production
 Mu2e - target size and material
were optimized at 8 GeV/c – 16
cm long, 0.3 cm radius gold target
 Secondary/tertiary interactions,
ionization energy losses could be
important for thick target. Thick
target effect is energy dependent.
 Full simulation of thick target is
needed to estimate low energy
pion yield at different energies
 Simulation code should be tested
in wide energy range
Pion Production- what energies and angles are important?
Stopped Muon Yield vs Initial Pion Kinetic Energy
~60% from 20-60 MeV kinetic energy
or p = 77- 143 MeV
100
10
1
0
40
80
120
160
200
240
280
320
360
400
440
480
520
560
600
Kinetic Energy (MeV)
Stopped Muon Yield vs Initial Pion Angle
300
Stopped Muons per 1E6 incident protons
Stopped Muons per 1E6 incident protons
1000
250
200
150
100
50
0
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
cos angle
Courtesy to Rick Coleman, Mu2e collaboration
Mu2e sensitivity to pion energy&angle
distribution
Courtesy to Rick Coleman, Mu2e collaboration
Fancy spectrometer data vs model predictions
Fancy spectrometer data vs MARS models.
Pion kinetic energy of 40 MeV corresponds to momentum of 113 MeV/c
HARP data.
Pion kinetic energy of 40 MeV corresponds to momentum of 113 MeV/c
MARS - dash-dotted lines
MARS - dash-dotted lines
HARP collaboration conclusion
HARP vs HARP-CDP
FANCY measurements and fit
• Pion yield was measured by
FANCY spectrometer at KEK
for p Al at 3 GeV/c and p Al, p
Pb at 4 GeV/c.
•
Pion kinetic energies were
from 100 to 850 MeV, angles from 36 to 90 degrees.
• Collaboration has fitted each
data set by two-fireball model
(6 parameters, with clear Adependence of each fireball)
Two-fireball model vs HARP data
Green line – fit of 8 GeV/c HARP data,
red line – renormalized fit of 4 GeV/c FANCY data
Large angles only -
Χ2/ndf
=0.94
All angles - Χ2/ndf =2.6
Two-fireball model vs HARP data
Large angles only - Χ2/ndf =0.93
All angles - Χ2/ndf =3.4
Low angle pion production
•
Negative pion yield was studied at 10
GeV/c using JINR 2-m propane bubble
chamber. Two tantalum plate (1mm
thick) were placed in working volume.
•
Differential cross sections of negative
pion and proton production were
measured in proton-carbon and
proton-tantalum interaction. Pion
kinetic energies - 0.080 to 3 GeV,
angles - 0 to 180 degrees.
•
Two-fireball fit of HARP 8 GeV/c
tantalum data (renormalized by ratio of
proton kinetic energies) agrees well
with this measurement at least for low
energy pions.
JINR data and two-fireball fits
Green line – renormalized fit of 8 GeV/c HARP data,
red line – renormalized fit of 4 GeV/c FANCY data
Two-fireball fit vs HARP data
Large angles only - Χ2/ndf =1.6
All angles - Χ2/ndf =1.6
Two-fireball model vs HARP data
Green line – fit of 3 GeV/c HARP data,
red line – renormalized fit of 4 GeV/c FANCY data
Large angles only - Χ2/ndf = 1.1
All angles - Χ2/ndf =1.2
Thick target effects - I
•
•
•
•
•
Mu2e target is long (16 cm of gold) .
It is about 1.6 nuclear interaction
length
Low energy pions could be produced
in secondary, tertiary … interactions
Pion with kinetic energies < 100 MeV
are mostly produced in primary proton
interactions and near elastic
scattering of low energy negative pion
Results obtained using MARS- default
and MARS-LAQGSM are similar
Low energy negative pion yield from
thick target with about 10% precision
is proportional to low energy pion
yield in proton-nucleus interactions
Thick target effects - II
• Mu2e target - gold, length is 16
cm, radius 0.3 cm. Gaussian
beam with σx= σy=0.1 cm.
• Mu2e mostly collects pion with
kinetic energies < 100 MeV
• Distribution of track length of
negative pion inside target has
maximum near target radius
• Distributions obtained using
MARS-LAQGSM and default
version are similar
• Due to ionization energy losses
energy of pion at target surface is
lower than at production vertex
Thick target effects - III
•
•
•
•
There are no experimental data on low energy
pion production (< 30 MeV) at proton
mometum 3-10 GeV/c
Most of pions with kinetic energies < 30 MeV
at production vertex are stopped inside target
Only 6-7% of pion with energy < 100 MeV at
target surface are produced by pions which
has energy < 30 MeV in production point
HARP collaboration measured yield of
pions with energy > 30 MeV in proton- nucleus
collision (production vertex) at proton
momentum of 3 and 8 GeV/c. This data could
be used to estimate ratio of low energy
negative pion yield at low and high proton
energy
Low energy pion yield
•
For comparison of yields from thick target
pion with kinetic energies > 30 MeV
should be compared. Pion with lower
energies are mostly stopped in target
•
Low energy negative pion production from
heavy target nearly linearly depend on
kinetic energy of primary proton
•
Low energy negative pion yield from
tantalum is larger then yield from carbon
at 3 GeV/c
•
Normalized low energy positive pion yield
is larger at 3 GeV/c than at 8 GeV/c
Conclusion
• Current versions of GEANT4 and MARS do not agree with data on
low energy pion production in energy range from 3 to 10 GeV/c.
FLUKA, PHITS ?
• Data on negative pion production looks like compatible, positive pion
production measurement HARP and HARP-CDP does not agree
each other.
• Experimental data on low energy pion production in energy range
from 3 to 10 GeV/c can be fitted by two-fireball model
• Calculation based on this model predicts nearly linear rise of
negative pion yield (< 100 MeV) with primary proton kinetic energy
and more weak energy dependence for low energy positive pions
Normalized per kinetic energy pion yield is larger at 2 GeV than at 8
GeV